Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$214.83	6.645%	$229.1055	$229.11	$229.10	$229.10
Purchase #2	$213.70	11.523%	$238.3247	$238.32	$238.30	$238.30
Purchase #3	$167.43	9.598%	$183.4999	$183.50	$183.50	$183.50
Purchase #4	$143.67	8.545%	$155.9466	$155.95	$155.95	$155.90
Purchase #5	$53.90	10.611%	$59.6193	$59.62	$59.60	$59.60
Purchase #6	$217.48	10.613%	$240.5612	$240.56	$240.55	$240.60
Purchase #7	$119.65	10.189%	$131.8411	$131.84	$131.85	$131.80
7 purchase totals =	$1,130.66		$1,238.8983	$1,238.90	$1,238.85	$1,238.80